I live in Northampton (UK), so we don't get very harsh weather often -
just the usual: rain one minute, bright and sunny the next!!

It's actually my folks who've asked me to do a bit of research, so
thanks very much for the quick responses. I'll pass on the
recommendations of getting a strong flexible pond liner, and laying it
over the top of the old one, rather than getting a preformed one.
Thanks a lot!

If anyone's got any further advice or recommendations, please keep 'em
coming!!

Tim.